Flotation machine



A: w. FA HRENWALD FLOTATION MACHINE Aug.'27, 1946.

Filed July 12, 1945 3 Sheets-Sheet 2 PUL'P LEVEL D m E R H H w R U. H mA INVENTOR ATTORNEY I PULP 0y;

Aug. 2-7, 1946; w, #AHRENWALD 2,406,532

FLOTATION MACHINE 7 Filed July 12,1943 3 Sheets-Sheet s 10/ RTHUR' w.FAHREuwAw V 25 INVENTOR Patented Aug. 27, 1946 UNITED STATES PATENTOFFICE FLOTATION MACHINE Arthur W. Fahrenwald, Moscow, Idaho ApplicationJuly 12, 1943, Serial No. 494,319

17 Claims.

This invention relates to afiotation machine useful in ore dressingprocesses wherein mineral bearing pulp is circulated, agitated andaerated to facilitate the separation and recovery of the variouscomponent elements.

Reference is made to my co-pending application, Serial No. 415,893,filed October 21, 1941, fora Flotation machine, now matured into UnitedStates Patent No. 2,337,806, patented December 28, 1943, of which thisapplication is a continuation-in-part. Also see my Patent No. 2,291,031,issued July 28, 1942, and entitled Flotation cell.

Th general objects of this invention are to provide a new and improvedmachine for the treatment of ore-bearing pulp whereby an increase inproduction relative to the conventional input of power is obtained;wherein a higher rate of mineral recovery per unit of cell volume ispossible over earlier equipment; wherein a higher grade qualityofconcentrate is produced or attained than has heretofore been thoughtpossible; and wherein a foolproof system of handling orebearing pulps isprovided to eliminate to a large extent the necessity of the exercise ofa high degree of human judgment in the operation of the machine.

The dressing of mineral pulps is not new and has been performed invarious ways by several types of machines, most of which employ a cellinto which and from which pulp is, moved and in which the movin pulp isaerated to produce a .froth that is skimmed to separate the concentratefrom the pulp'residue passing on. One of the earlier practices thatIhave determined to be bad in principle and inefficient in operation isthat accompanying the operation of flotation cells wherein pulp and theincoming air is jointly fed to the impeller through a stand pipe closeto the axis of the impeller hub and around the shaft thereof. Thiscondition is impracticable and objectionable for several reasons and itis an important object of this invention to provide mechanism to curethese conditions, which are, generally, a strangulation of air intakedue to uneven pulp flow blocking theair intake, thus producing unevenaeration, undesirable pulp and air centrifuging, improper pulp swirls inthe cell, and unnecessarily high power consumption. The feeding of pulpat or near the hub of the impeller is improper because of the slowlineal velocity of the: blades of the impeller and their consequentinability to properly impartforce and pressure to the pulp.

In accordance with my invention, this machine provides for theintroduction of both original and recirculatory pulp in a gravity flowthat reduces power requirements, and it also includes the-introductionof the two prime elements, pulp and air, to the cell and its impellerthrough a separate and distinct passageway for each. Further advantagesare gained by sequentially delivering first the air and then the pulp tothe impeller at different portions thereof. This feed is accomplished byleading the air to the impeller at its hub where the impeller bladesmost naturally receive the air and impart velocity to it, while the pulpis delivered to the impeller blades at a point where their peripheralvelocity is greater than at the hub and they are better adapted to actupon the semi-solid matter in producing its aeration. By the actualscientific comparison of the present machine with those of the earlierart, it is possible to accurately measure the advantages gained by thisnew principle of pulp and air feed. I have done so and the results showthat aeration can be doubled in this machine with a, given volume ofpulp over the aeration accomplished where both pulp and air are fedsimultaneously to the impeller hub.

These advantages are partially due to the increased air moving capacityof the impeller blades that are thus freed at their axial ends to biteinto the air and start it'into high velocity movement, and also to themore eflicient application of forceto th -incoming stream of pulp. Inaddition, this principle eliminates the formation of undesirable vacuumpockets that may form in the earlier machines and retard and disrupt theoperation thereof.

I have also been able in this machine to prevent the formation of avacuum under the impeller which normally draws gangue thereunder toincrease the resistance against rotation of the impeller. In addition, Ihave made it possible for the space under the impeller to be filled withaerated pulp having a low viscosity and consequently less resistance tothe impeller.

According to the preferred embodiment of my invention I provide a cellstructure adapted to contain fluid pulp and having suitable pulp inletand outlet openings as well as a froth overflow lip to a froth launder.This cell may be used singly or in multiples in series and their use ispermissible in every type of mineral recovery circuit. Since theindividual cell contains the nucleus of the inventionas well as itsappurtenances, I shall confine this description to a single cell. Uponsuitable structural support memhers I mount a cylindrical beam whichforms-the backbone of the moving parts of th cell, priand the aerationof the pulp fed thereto.

'3 r 'marily to support the upright shaft that carries the impeller inrotation, the drive means for this shaft, andthe bearings in which thisshaft is journalled.

As is customary, the impeller, which has upperv blades, is disposed inthe cell adjacent'its floor and usually coincident with the verticalmedian of the cell. The impeller consists of a, horizontal plateattached to a shaft rotatable in a vertical axis. Upon thetplateareblades that radiate from the axis toward the edge and provide duringrotation the draft for the air inlet column The plate is slotted atseveral placesgso'that there is communication from abovetobelow theplate,

the under side of which also hasminorblade' elements to aerate the pulpthat may be located under the impeller and to, at the same time,

destroy any vacuum that otherwise would exist below the impeller disc ifit were solid.

' lated is controlled by means of suitable gates or {I surround theimpeller with a plurality of pulp to the impeller blades atapproximately onehalf th'e'distanoe from the hub to their outer ends,For convenience I have found it desirable to support thestructureforming the pulp feed chamber upon the deflector blades and incertain cases' these blades are attached to and form integral legs forthis chamber structure. An inlet' to "the pulp feed chambe is arrangedwith a conduit to receive pulp entering the cell pulp inlet in the'wallthereof and, on occasion, a recirculatory feed of pulp may be permittedfrom a pulp return trough of V-shape and contiguous in measuredquantities. V

Abovethe' aforementioned chamber is an accumulator chamber fortheoutgoing pulp from the cell. These two chambers are preferably diswith'the cell and which receives overflow pulp tinctfrom each other and thelatterha an outlet coupled with 'the outlet'opening of the cell. Risingfrom the accumulator chamber is'a col- 'umn havi'ng'an overfiowlip foroutgoing pulp and the lip of this column may be'formed as a verticallymovable sleeve to vary the relative height of the lip above the flow todetermine the pulp level of the cell.. Means are provided 'for themanual movement of this sleeve from exterior of the cell. The overflowlip is surrounded by a bafile that rises from a point below thepulplev'el in the cell to abovethe level of the froth that forms uponthe fluid pulp within the-cell; A rotary froth paddle, adjustable as toits radius of sweep, is mounted on the cell in aposition to assist the"froth over the froth overfiowlip and into the launder. To facilitatethe recirculation of pulp in an t V cumulator chamber as -we1l as thepulp feed chamber and the'passage'of pulp thusrecircue individual cellor in combination with other similar cells, I employ the pulp returntrough mentioned above which'is V-shaped and formed on "a side of thecell preferably below the portion of. thecell over which the outgoingfroth passes. Conduits as desired are connected with the acother valvingelements. a

' The'novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both'as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of a specificembodiment when. read in connection with V the accompanying drawings, inwhich --Figure 1 is a view in elevation of a pair of flotation cellsembodying my invention, which View has portions broken away and othersshown in section for convenience of illustration; Figure 2 is a verticalsectional view of 'a cell showing the general interior arrangement ofparts as taken on lineZ-Z of Figure 1;

Figure 3 is a plan view 3-3 of Figure 1; Y

Figure 4 is a plan view in section taken on line 44 of Figure'l;

Figure 5 is a perspective view of the impeller employed in my flotationcell;

Figure 6 is a sectional view taken on line fi -fi of Figure 1; V I

"Figure '7 is an enlarged detailed sectional view of-the impeller-and ofthe pulp feed chamber and air conduit illustrating the flow of materialand its mixing andaeration in my flotation cell Figure 8 is afragmentary perspective. view of a deflector plate employed at thedischarg of the impeller; and a v 1 Figure 9 is an upright diagrammaticviewof a cell embodying my invention and illustrating the principle ofoperation thereof.

A preferred embodiment of my inventionfre ferring to Figures 1 and 2 ofthe drawings, is constituted by a cell into which are placed theoperating elements for the reception, aeration, and the passing on ofmineral'bearing pulp. Acell is made up of a plurality of wallsincludingthe bottom l0, back wall l2, front wall I2 andside walls I3.When a-plurality of cells are operated together, usually one 'of theside walls fornis a common "wall between adjacent cells. The'front wallhas an overflow lip I5 across which the froth produced in thecell passesinto a suitable launder (not shown). Supported at' its'ends above thecell' is a longitudinal beam I6, here shown as tubular in shape. Uponthis beam and over each cell 1 mount a quill-bearing iuwhich 7 receivesand supports the impeller shaft or spindie 23 for rotation. *Alsomounted upon the beam I6 is asuitable motor base 19 to which motor 23maybe attached. Between the sheave 2| of the motor and a driven sheave22 on the shaft 20 is drive belt 24,'whereby rotary motion. istransmitted from the motor to the impeller shaft. An impeller,designated' as a whole by the numeral 26, is shown in FigureS 'tocomprise a base plate 28 that is secured to the bottom end of the shaft20 and supports on its upper face a plurality of radiating blades 29.The inner ends of the blades 29 are preferably spaced ashort distancefrom the shaft 20 for a purpose later to be described. At suitableplaces aro n h ripher'y of the plate 28 810115 30 are formed therein andadjacentone side of the slots 30, preferably on its trailing edge, inthe normal direction of rotation, is a, buttressed blade-or vane 3|;that extends axisward of the impeller at; least the length of the slot30.

- =-During the operation of the cell, air is con- -ductedto a'pointadjacent the hub'of theimin section taken on line peller andiinterior ofthe ends of' the bladest'29 by means. of the air conduit 34 which rises;from a point directlyabove the impeller to about the mid-portion of thecell vertically. Surrounding this air conduit is a cylindrical walledwhich has a bottom 3'1; and intermediate divider wall 38 which separatesthe annular spaced enclosed around the conduit 34 into a feed chamber 49and a pulp accumulator chamber 42-.

Pulp is fed to the chamber 48 by the conduit 41 and pulp is withdrawnfrom the chamber 42 by the conduit 43. Pulp is delivered from externallyof the cell to the conduit through the connector 44 and pulp passes fromthe conduit 43 to externally of the cell through the connector 45. Pulpmay also be introduced from the cell into the connector 44 by means ofthe by-pass opening 46.

The bottomv wall 31 of the chamber 40 is ported as shown in Figure 6byseveral openings 41 which are arranged to discharge pulp to theupright blades of the impeller in approximately the mid-portion thereof.

The structure forming chambers =4!) and. 42 and including the conduit 34is supported above the impeller and above the floor of th cell by meansof inverted L-shaped legs 53 which rise from a base or wear plate 5!. Aplurality of these legs are arranged around the periphery of theimpeller in radial fashion and serve to deilect discharge aerated pulptherefrom into upwardly directed paths of travel. Since the action ofthe discharging pulp upon the deflector legs 50 is abrasive, I protectthem by individually removable sheaths 52 which may assume the form ofU-shaped clips of wear-resisting material such as rubber or hard iron orthe like.

The upper portion of chamber 42 isclosed by a cover 54 having a sleeve55 rising therefrom and. forming a pulp overflow throat in the mouth ofwhich is positioned a vertically adjustable sleeve 55 the upper lip ofwhich determines and defines pulp level within the cell. It ispreferablethat the overflow lip 56 be. cylindrical so that it is substantiallyaxial of the cell proper.

, The sleeve 55. is vertically adjustable and this adjustment isattained by attaching to the legs 58 a yoke 59 which is raised orlowered by the v action of the screw 60 mounted in the bracket 6|.v Thescrew is raised or lowered by the hand wheel 62 when turned. The bracket6 t is secured to a cylindrical bafile 63 which surrounds the overflowlip of sleeve 56 from a point substantially below the pulp level to apoint above the froth within the cell. Sleeve 63 is rigidly mounted uponthe sleeve 55 by means of fillets 6. as shown in Figure 6.

. Froth overflows across lip. I5 from the cell under the urgence of'thefroth paddle 10 mounted on arm II which is swung bythe rotary shaft 12turned by motor I3. V

It will be seen that the front wall l2 of the cell which slopesoutwardly as it rises has interiorly thereof a septum l5 rising from thebottom of the cell upwardto the pulp level. septum 15, whose heightisabout two-thirds of the depth of the pulp, is ported at 16 and the size'of this port may be varied by movement of the gate 11 that is mountedfor verticallyadjustable positioning by means of "the arm '18 and pin19. From the port 16 to the interior of chamber a conduit 80 is providedfor the con- .veying of pulp from the V -shaped settling chamber 82formed-between walls. 12- and 15 into the pulp feed chamber above theimpeller.

Method of operation- This flotation machine operates according "to thewell-known phenomena underlying the 'pro- 'cess of froth flotation. Airbubbles are introduced into a preparedpulp containingfinely pulverizedore particles suspended in water. Upon the contact of the air bubbleswith certain mineral particles the latter are attracted to and willadhere upon the skin of the bubbles and be levitated through the pulpbody to the surface where a froth is formed and skimmedv forthe recoveryof the thus accumulated values. It is well known that by thediscriminate 'use of various flotation reagents the air bubbles can bemade particularly attractive to certain values in the pulp while otherswill notadhere and will remain suspended in the pulp body for passage toother cells for recovery there or for ultimate disposal in any mannerdesired' Bothbulk and differential flotation can be accomplished in theinvention here described with the advantages set forth above. a

My machine improves. the present modes'of flotation cell operation andfunction by providing means whereby better air-bubble mineral particlecontact is effected toproduce a more discriminate froth having better 1particle-suspending properties and the mineral bearing pulp from which adesired value has been withdrawn by the air bubbles is thereafterhandled in a manner that enhances froth formation while at the same timeit does not interrupt it or destroy the bubbles by cross currents thathave an abrading and deleterious action on. the froth. In my machine itwill, be apparent that I employ sub-aeration of the pulp with the airbeing drawn or forced to the impeller at the hub thereof while the pulpis fed to the impeller at about the middle of the blades of the impellerto produce a better air-bubble formation. an improved mechanical pulpdispersion, and a highly improved air-bubble mineral particle contact.

Pulp is fed to the cell through the connection M and conduit. ll intothe feed chamber 49 which is toroidal in shape and issupport'ed'directly above the impeller 26; Air is passed directly to thehub of the impeller through conduit 34 which descends throughthe centralopening of the torus shaped feed chamber but out of communication withthat chamber. The blades of the impeller, being such that their inner oraxisward ends are spacedfrom the hub or shaft of the impeller, easilybite into and scoop the air delivered thereto through conduit 34 andstart that air into high velocity'movement outward of the impellerwithout interference in its initial movement from pulp as is so oftenthe case with those cells wherepulp and air are fed. together.

Pulp from the chamber. 40 is delivered to or deposited upon theblades ofthe spinning impeller at points outward of the air pickup zone throughthe openings 41. It will be recognized that the speed of the impellerblades at the greater radius a where the pulp is deposited is severaltimes that at the hub radius which is smaller. Thus air is startedfreely into movement between the imeller blades while the blades outwardof the h b are'striking the streams of descending pulp at high velocitywhich in normal operation can be some 6000 times per minute. The effect.is to .finely disperse the pulp instreams of air. and,

- modes of operation.

19116105156 with conventionalcells,

. 7 7 ours and particle adherence and levitation begins, with aerationbeing materially increased over that of conventional cells of differentstructure and In'addition to the above mentioned operation of theimpeller, there are other functions provided by the slots 30 and theminor blades 3| on the lower side of the impeller plate 28. The impellerrotates in a clockwise direction as viewed in Figure 5 and thus theslots 30 trail the blades 29 and 3|. While in unslotted blades it-iscustomary for a vacuum to form under the impeller, with this arrangementany material drawn under the impeller is frothed and dispersed. Theresult is in operation atotally free impeller not operating against ahighly viscous mass of pulp drawn thereunder as is true in theconventional machines.

, Asthe dispersed airfand pulp is ejected from the impellerit isdeflected by blades so in a manner to collimate it and prevent swirlingor boiling and by thus being deflected it immediately begins I theupper. surface of the settling chamber 82' its ascent through the pulptoward the surface of the cell where the froth is formed. 7

As illustrated in Figure 9, the mineral particle pulp bear'ing airbubbles leave the impeller and rise through the pulp body in the celltotward the surface. Sinceejection is all around the periphery of theimpeller there is a cylindrical sheet of potential froth rising in thepulp around the central feed and the accumulator chamber toward thesurface of the cell. Axisward of'this rising froth potentiation is thepulp withdrawal port between the baffle 63 and the exterior walls of thethroat formed by members 55 and 56. The outgoing pulp passes throughthis port evenly all around the cell interiorly of the rising frothpotential in'a manner that avoids cross currents and at a station thatis subsequent in the course of travel ofthe pulp with respect to thestation at which'the froth leaves the pulp and forms on. the pulpsurface. 'In effect the pulp course is a' closed circuit that providesvery definite advantages in the cell operation. It can be definitelystated that this arrangement provides an in.- creased rate of mineralrecovery because the air bubbles reach the surface faster with lessabrasion than is the case with cells wherein there ar counter-currentsbetween the pulp and the bubble flow. My cell is further marked in itsoperation by a complete absence of eddying currents, pulp boiling andbubble centrifuging, and all well known to'bel load conditions inflotation practices. The pulp level within the cell may be varied byvertical movement of the overflow lip 56 through V the raising orlowering of the yoke 59 under the action of the screw 60 produced bymanual operation of handwheel 62. 'The position of lip 56 is largelydetermined by the nature of the ore pulp being handled and othercircumstances such as V timeand rate of recovery desired in a particularcell. l

' As pulp overflows the lip 56 it descends through V the throat 55 intothe accumulator chamber 42' and thence outward of the cell throughconduit 43 and connector 45 where it maydischarge into an adjacent cellor be passed along in the mineral recovery circuit in accordance withflotation practices. v V i going pulp is not permitted to flow to theimpeller again. While air also passesdownward through throat to the airtube 3 4'the relative size of the two is. such that the sheet ofdescending, pulp clinging close to the inner wall of the throat does notinterfere with the air stream as so often is It is tobe notedthat theout- 'Froth that accumulates on the surface of the pulp is drawn offthecell along one side thereof largely by gravity and assisted by the.rotary. froth paddle 10. As the froth overflowslip I5 it may bedeposited 'in a launder or other disposal means as is convenient ordesirable. It should be noted that the froth passes .over

formed to one side of the celljust priorto the overflow of the frothfrom the cell. In' this passage over chamber 82 the only mineralcontent, that can return to theimpeller must descend or settle throughthe relative still pool of the chamber, then only after it has made acomplete circuit of the cell. In other'words, there is no shortening ofthe recirculatory pulp from the impeller through the pulp mass and backto the impeller with an avoidance of its travel through the entire frothformation circuit. Such pulp as passes through chamber'BZ is returned tothe feed cham I ber 40 by way of conduit 80 under the control of abovesaid impeller for delivering air to the hub of the impeller, radialdeflectors surrounding said impeller, a pulp feed chamber above saidimpeller surrounding the lower end of the air tube and having outletsfor delivering pulp to the impeller radially outward from andindependently of the air supply thereto, meansfor conveying incomingpulp from the tank inlet to the feed chamher, a pulp accumulator cupabove said feed- 7 chamber and around the air tube, the upper edge oftheaccumulator cup defining the pulp level said tank, a ballle surroundingsaid lipfrom a point therebelow and extending above the froth formed onthe pulp in the tank, meansfor conducting pulp accumulated in said cupto exterior of the tank throughthe pulp outlet, a settling chamber insaid tank and havingits open mouth below the pulplevel and under thefroth just prior toits passage to the froth overflow lip of the tank,and means for conveying pulp from said settling chamber to the pulpchamber. '2. A flotation machine, comprising: a tank having pulp inletand outlet openings and a froth ,overflowlip, an impeller rotatable inthe lower portionof the tank, an air tube rising axially above saidimpeller for delivering air to the hub of the impeller, radialdeflectors surrounding said impeller, a pulp feed chamber above saidimpeller surrounding the lower'end of the air tube and having outletsfor delivering'pulp to'the impeller radially outward from andindependently of the air supply thereto, means for conveying.

incoming pulp from, the tank inlet to the feed chamber, a pulpaccumulator cup above said feed chamber and around the air tube, theupper edge of the accumulator cup defining-the pulp level lll saidtank,a battle surrounding said lipfrom a pointtherebelow and extending abovethe froth "formed on the pulp in the tank, means for conducting pulpaccumulated in said cup to exterior of the tankthroughthe pulp outlet, asettling chamber in said tank and having its open mouth below thepulplevel and under the froth just prior toits passage to. thefrothoverflow lip of .outward from their inner ends and independently ofthe air supply thereto, means for conveying incoming pulp from the tankinlet to said chamber, and means for gathering pulp leaving the tank andfor conducting itto the pulp outlet from the tank.

4. A flotation machine comprising: a tank having pulp inlet and outletopenings and a froth overflow lip, an upwardly directed blade impellerrotatable in the lower portion of said tank means for rotating saidimpeller, an air tube rising above said impeller axially thereof, a pulpfeed chamber above said impeller and surrounding the lower end of saidair tube, said feed chamber having outlets for delivering pulp to theimpeller blades outward from their inner ends and independently of theair supply thereto, means for conveying incoming pulp from the tankinlet to said chamber, and means for gathering outgoing'pulp axially ofthe tank and for conveying it to the pulp outlet of the tank.

5. A flotation machine, comprising: a tank having pulp inlet and outletopenings and a froth overflow lip, an upwardly directed blade impellerrotatable in the lower portion of said tank means for rotating saidimpeller, an air tube rising axial- 1y above said impeller, a toroidalshaped pulp feed chamber surrounding the lower end of said air tube andhaving a bottom wall provided with a ring of openings spaced outwardlyfrom the lower discharge end of the air tube and located to deliver pulpto the mid-portions of said blades, a pulp conduit from the tank inletto said feed chamber, and means for gathering pulp leaving said tank andfor conducting it to the pulp outlet from the tank.

6. A flotation machine, comprising: a tank having a froth overflow lip,an upwardly directed blade impeller rotatable in the lower portion ofsaid tank means for rotating said impeller, an air tube rising axiallyabove said impeller, a toroidal shaped pulp feed chamber surrounding thelower end of said air tube and having a bottom wall extending outwardfrom the air tube and a downwardly directed outlet to the impeller at apoint spaced outwardly from the inner wall of said chamber and locatedto deliver pulp to the mid-portions of said blades, means for conveyingpulp to said feed chamber, means for gathering pulp leaving said tank, asettling chamber in said tank below the froth overflow lip and overwhich outgoing froth flows to said lip, and a spigot for said settlingchamber.

'7. A flotation machine, comprising: a tank having a froth overflow lip,an upwardly directed blade impeller rotatable in th lower portion ofsaid tank means for rotating said impeller, an air tube rising axiallyabove said impeller, a toroidal shaped pulp feed chamber surrounding thelower end of said air tube and having a bottom wall extending outwardfrom the air tube and a downwardly directed outlet to the impeller at apoint spaced outwardly from the inner wall of said chamber and locatedto deliver pulp to 10 the mid-portions of said blades,.means forconveying pulp to said feed chamber, means for gathering pulp leavingsaid tank, a. settling chamber in said tank below the froth overflow lipand over which outgoing froth flows to said lip, and a spigot for saidsettling chamber to convey .pulp settling therein to the feed chamber.

8.. A flotation machine, comprising: a tank having an upwardly directedblade impeller in the lower portion thereof, means for axially feedingair to said impeller, means for feeding pulp to said impeller outwardfrom the air feedthereto and midway of the impeller blades, meansforcentrally gathering pulp from said tank above the impeller and forconveying it exteriorly of the tank, a settling chamber in said tank toone side of the impeller and below the pulplevel of the tank, a conduitfrom the settling chamher to the primary pulp feed means for theimpeller, a bypass conduit from the settling chamher to the primary pulpfeed means, separately operated valves for eaohiconduit, and anoverflowlip in the wall of the tank toward "which froth flows in passingover the settling chamber.

9. In a flotation cell, an impeller, comprising: a base plate, a singleset of uncovered blades extending from the axis of the upper surface ofsaid base plate, each blade on its axisward end a being free from theothers, means'iorv supplying air to said blades at their free ends,means for independently supplying pulp to said blades at a pointintermediate their ends and outwardly from the air supply thereto, andmeans for rotating said impeller.

10. In a flotation cell, an impeller, comprising: a base plate, a singleset of uncovered blades on the upper surface of said base plate, eachblade being radial of the axis of the base plate and having its axiswardend free from the other blades, means for supplying air to said bladesat their free ends, means for independently supplying pulp to saidblades at a point intermediate their ends and outwardly from the airsupply thereto, and means for rotating said impeller.

11. In a flotation cell, an impeller, comprising: a base plate, a singleset of uncovered blades extending from the axis of the upper surface ofsaid base plate, each blade on its axisward end being free from theothers, said base plate having slits therethrough closely adjacent thetrailing side of certain of the impeller blades, means for supplying airto said blades at their free ends, means for independently supplyingpulp to said blades at a point intermediate their" ends and outwardlyfrom the air supply thereto, and means for rotating said impeller.

12. In a flotation cell, an impeller, comprising: a base plate, a singleset of uncovered blades extending from the axis of the upper surface ofsaid base plate, each blade on its axisward end being free from theothers, said base plate having slits therethrough closely adjacent thetrailing side of certain of the impeller blades, minor blades on theunder side of, the impeller base plate in advance of said slits, meansfor supplying air to said blades at their free ends, means forindependently supplying pulp to said blades at a point intermediatetheir ends and outwardly from the air supply thereto, and means forrotating said impeller.

13. An impeller, comprising: a base plate, a single set of uncoveredblades extending from the axis of the upper surface of said base plate,each blade on its axisward end being free from the others, said baseplate having slits therethrough closely adjacent the trailing side ofterrain ofithe impellerblades. V. V

' 14. .An impeller, comprising; a base plate, a single set of uncoveredblades extending from the axis of the upperrsurface of said base plate,each blade on its axisward end being free from the others, said baseplate having slits therethrough'closely adjacent the'trailing side ofcertain of'the impeller blades, and. minor blades on the under'side ofthebase plate in advance of said slits.

1 5. In a flotation cell, .a rotatable impeller in for rotating thesame; above said impeller, an air tube having a lower discharge openingaxially adjacent the upper surface ofthe impeller; walls forming anannular pulp feed chamber surrounding said air tube above the impeller;a supply conduit from 'exterior of said cell to said iorming a sleevebaflle aroundlthe lip of'sa'id cup rising from a point therebelow toabove the froth surface Within said cell.

the lower portion of the cell and including means 7 16. A flotationmachine, comprising: a tank having pulp inlet and outlet openings and afroth overflow lip, an impeller. rotatable in the lower portion of saidtank and comprising arplate having upwardly directed uncoveredbladeameans for rotating said impeller, an air inlet tube rising abovesaid impeller co-axially thereof to deliver incoming air to the axiswardportions of said blades, a pulp feed chamber above said impeller andaround, said air inlet tube and having outlets above the edges of saidblades between their axisward and outwardportions for delivering pulpthereto independently of the air supply, means for conveying incomingpulp from the tank inlet to said feed chamber, and means for gatheringpulp to leave said tank' and for conducting it to the pulp outletopening therefrom;

17. Ina flotation machine, sub-surface aeration mechanism, comprising:an impeller and m'eans for rotating the same, said impeller havingupwardly directed uncovered blades radiating from the impellers axis,means for delivering air to the axisward portions of said impellerblades, and means for delivering fluent material to be aerated to saidblades at stations located'intermediate the ends of said impeller;blades and outward in spaced apart relation from the point of deliveryof the air.

ARTHUR

